1. Field of Invention
The present invention relates to a gamma correction device, method thereof, and display apparatuses including a gamma correction device.
2. Description of Related Art
Various types of flat panel display apparatuses are widely used. Generally, flat display apparatuses are classified into emissive and non-emissive display types. Light-receiving (e.g., non-emissive) display apparatuses include liquid crystal displays (LCDs), while light-emissive display apparatuses include plasma display panels (PDPs), electroluminescent displays (ELDs), light emitting diodes (LEDs), vacuum fluorescent displays (VFDs). LCDs are most widely used in application with mobile apparatus on the merits of high picture quality, lightness, thinness, and low power consumption.
FIG. 1 is a functional block diagram of a general LCD apparatus 100, illustrating a schematic architecture applicable to a mobile unit. Referring to FIG. 1, an LCD apparatus may include an LCD panel 10 displaying image signals, and an LCD driver 190 applying drive signals to the LCD panel 10.
LCD panel 10 may be a unit constructed with a pair of transparent substrates between which liquid crystals are injected. On one of the two transparent substrates, gate lines may be arranged at constant intervals. Data lines may be arranged at constant intervals perpendicular to the gate lines. At regions corresponding to intersections between gate lines and data lines, thin film transistors may be arranged in matrix patterns. Each thin film transistor may correspond to a pixel. Color filters of red (R), green (G), and blue (B) may be arranged on other regions of the substrate. On a back side of the LCD panel 10, a backlight (not shown) may be arranged to provide a uniform light source for the LCD panel 10. For example, a light source for the backlight may be used with a cold cathode fluorescent lamp (CCFL).
An LCD driver 190 may include a plurality of control circuits, for example, a gate driver 20, a data driver 30, a timing controller 40, a gamma correction voltage generator 120, a gray-scale voltage generator 150, etc. In a mobile unit, an LCD driver 190 may be a single chip.
A timing controller 40 may generate control signals (e.g., a gate clock, a gate-on signal, etc.) required for operating a gate driver 20 and a data driver 30 in response to a clock signal CLK. A gray-scale voltage generator 150 may output a plurality of gray-scale voltages Vg used as references for generating LCD drive voltages. A gate driver 20 may scan pixels of an LCD panel 10 by a line in sequence. A data driver 30 may generate LCD drive voltages, corresponding to color signals RGB provided by a timing controller 40 in response to gray-scale voltages Vg provided by a gray-scale voltage generator 150. LCD drive voltages generated by a data driver 30 may be applied to an LCD panel every scanning cycle.
Conventionally, a characteristic of light transmittance in a liquid crystal is not linearly related to voltage levels, and brightness for input gray scales is linearly varied. In other words, if image data is varied and/or the brightness (e.g., luminance) of a backlight is varied, the picture quality appearing on an LCD apparatus 100 may be varied. Thus, a gamma correction voltage generator 120 may control contrast and brightness for images by regulating gamma characteristics to offer improved and/or optimum picture qualities based on operational conditions. A conventional LCD apparatus 100 as shown in FIG. 1 may perform gamma correction by modifying the gamma voltage, for example.
A gamma correction voltage generator 120 may output a plurality of the gamma correction voltages (e.g., eight in number) as a result of regulating gamma characteristics. A gray-scale voltage generator 150 may receive gamma correction voltages from a gamma correction voltage generator 120 and/or generate gray-scale voltages Vg with more defined voltage levels (e.g., 64 levels). A technique for regulating the contrast and/or brightness of pictures by means of gamma characteristics in an LCD apparatus 100 is referred to as ‘gamma correction’. Gamma (γ) is a gradient of a line representing an input value vs. an output value of data. The output value is defined by a relation of (Inputvalue)1/γ. For example, if a gamma value is 1.0, there is no variation in the input value (i.e., null transformation). If a gamma value is larger than 0.0 and smaller than 1.0, the picture is dimmed. And, if a gamma value is larger than 1.0, the picture is brightened.
A way to provide gamma correction is to apply gamma values fixedly assigned to various types of displays in order to correct input/output characteristics of a display apparatus. For example, the National Television System Committee (NTSC) provides televisions operable at a gamma value of 2.2, while the Phase Alternate Line (PAL)/Sequential Color and Memory (SECAM) provide televisions operable at gamma value of 2.8. Gamma correction voltages corresponding to a gamma value (e.g., output luminance values for input gray scales) may be arranged in a lookup table LUT. The values stored in the lookup table may correspond with gray-scale voltages.
However, because a gamma correction scheme as described above uses a fixed gamma value, it is difficult and/or impossible to adapt for variations in image data and brightness of a backlight (e.g., variations in displaying environments). In order to overcome these problems, a gamma voltage generator 120 may have a plurality of lookup tables corresponding to a plurality of gamma values. However, as lookup tables need to store offset values for all gray-scale voltages, it may be necessary to prepare numerous registers, which may increase chip size.
Furthermore, to provide lookup tables for various gamma values, a manufacturer has to measure gray-scale values that correspond with each gamma value to be stored in registers. Therefore, as a number of gamma values increase, time and costs for determining values to be stored in registers increases.